Applications Of Graphene Oxide In Anti-corrosion Coatings For Metals And Its Dispersion Mechanism

Corrosion protection is one of the most important research topics in the development and use of metal materials,which has great economic value and significant social benefits.At present,traditional corrosion protection methods,such as phosphating coating and organic anti-corrosion coating,cannot cope with the complex application environment of metal due to the backward technology and poor performance,nor can they meet the increasingly stringent environmental protection laws and regulations.Graphene oxide?GO?,as a new nanomaterial,has new structures and characteristics different from those of previous nanomaterials,especially its special two-dimensional layered structure and excellent barrier properties,which has potential applications in the preparation of corrosion protection coatings.However,GO is often suffered from similar dispersibility problems as traditional nanomaterials in applications.Besides,due to the large specific surface area and special surface chemistry brought by its special structure,the dispersion/agglomeration mechanism of GO is different from that of traditional nanomaterials.Therefore,this thesis focuses on the above problems faced by GO,and explores the application of GO in the development of new anti-corrosion coatings from the perspective of improving the corrosion resistance of materials.Meanwhile,from the perspective of the dispersion/agglomeration behavior of nanomaterials,the difference between the self-assembly behavior of two-dimensional GO sheets and traditional gold nanoparticles is compared,and the effects of surface chemistry of nanomaterials on their self-assembly behavior and the mechanism of action is studied,so as to reveal the internal dispersion and stability mechanism of nanoparticles.The main contents are as follows:?1?GO was introduced into the traditional chemical phosphating process to observe the surface morphology evolution of phosphate coating during the phosphating process.The effect of GO on crystal growth,structure and composition during the phosphating process was systematically studied.Results showed that GO was an effective accelerator and modifier that can significantly accelerate the phosphating efficiency and improve the quality of the phosphate coating,forming a denser phosphate coating with smaller crystal grains and finer structure.And then the mechanism of GO in improving the phosphating process was proposed and discussed.Electrochemical tests showed that GO modification can improve the corrosion protection performance of phosphate coating due to the formation of denser coating and the co-deposited GO sheets that covered the pores in the coating,as a result,the corrosion rate of the phosphate coating was reduced by an order of magnitude compared with the traditional chemical phosphate coating.?2?The application of GO in the cathodic and anodic phosphating process was explored.The results showed that GO would be adsorbded continuously on the metal substrate during the anodic phosphating process,hindering the phosphating reaction;in contrast,in the cathodic phosphating process,GO changed the composition and structure of the crystals in the phosphate coating due to a different phosphating mechanism.The effects of current density and GO concentration on the crystal structure and composition of the phosphate coating during the phosphating process were systematically investigated.It was found that the lamellar structure of GO combined with its carboxyl groups and charging state on the surface of GO affected the ion migration on electrode/electrolyte interface during the cathodic phosphating process,which was more conducive to galvanizing reaction and thus changed the composition of phosphate coating.The anti-corrosion performance and protection mechanism of the phosphate coating were changed due to the co-deposited metallic zinc,electrochemical results proved that the cathodic phosphate coating had better corrosion resistance as a result of the sacrificed reaction of zinc.?3?The ammonium grafted GO sheets?AGO?were prepared by two-step chemical grafting reaction,which changed the surface chemistry of GO sheet.And then a new idea was proposed and then demonstrated to successfully address the compatibility issue between the epoxy resin and polyamine curing agent molecules in water system via utilizing the amphiphilicity of AGO.As a results,the problems during the curing and film-forming process due to the poor compatibility of water-borne epoxy?WBE?coating was successfully solved,and the generation of micropore defects in the coating film was effectively inhibited;while the AGO sheets were uniformly dispersed into the coating at the same time,obtaining a denser and more uniform film,which dramatically improved the corrosion resistance by three orders of magnitude.?4?Self-asembling of GO/rGO sheets to prepare graphene hydrogel was carried out via the chemical reduction of GO.The pore structure of the hydrogel can be controlled by simply adjusting the pH value of the GO dispersion,the pose size was gradually increased as the pH value increased.The relationship between the pH value and the surface chemistry of GO/rGO sheets was discussed,and the mechanism regarding controlling the self-assembly behavior of GO/rGO sheet was investigated.It was found that the electrical double-layer?EDL?interaction between GO/rGO sheets caused via the carboxyl ionization was the main force that stabilized the GO/rGO dispersion,thus changing the pH value can affect the ionization of carboxyl groups and then changed the EDL interaction relatively.As a result,the self-assembling behaviour of GO/rGO sheets can be adjusted to control the pore structure of the hydrogel.Rheological and electrochemical studies showed that smaller pore size and denser pore structure afforded for higher mechanical strength,while the cooperation of small pore and large pore was the key to enhance the electrochemical energy storage properties of graphene hydrogel.?5?High aspect-ratio 3D nanoporous gold was prepared via the self-assembly of calixarene capped gold nanoparticles using H₂ bubble as a template.And then different surface treatments were applied to remove calixarene ligands on the surface of nano-gold,showing that only UV/Ozone treatment could remove organic ligands and maintain the original 3d porous frame structure at the same time.XPS results proved that phosphine oxide was formed on the nano-gole surface after UV/Ozone treatment,which was the reason to maintain the stability of the 3d nanoporous structure.The electrochemical experiments showed that the UV/Ozone treatment can increase the electrochemical active surface area of the gold nanoparticles self-assemblies,but was detrimental for the electrochemical detection of nitrobenzene in water.While the calixarene capped gold nanoparticles self-assemblies showed great electrochemical response to nitrobenzene with a linear detection range of 17 uM-2.6 mM,as a result of the strong interaction between calixarene ligands and nitrobenzene molecules in water.